The present invention relates to a bone anchor, in particular, but not exclusively, to a bone anchor for graft fixation such as tendon or ligament fixation.
Due to increasing involvement of people with active sport, injuries are becoming increasingly common where tissues such as ligaments or tendons tear or detach from bone. Surgical techniques have been developed to reconstruct such torn soft tissues and to re-attach them to the relevant bone. One of the most common types of such injuries is tearing of the Anterior Cruciate Ligament (ACL). The Anterior Cruciate Ligament connects the femur to the tibia at the centre of the knee joint. Reconstruction of such tissues generally involves replacement with a graft such as autologous or artificial tendon. An autologous tendon graft may be taken from the patients patellar tendon or, alternatively, the semitendinosus may be utilised. A typical fixation technique involves the use of a circular button fixation device which is located on the outside of the femur above the knee. As this is some distance from the site where the graft will be utilised in the knee joint, sutures are used to attach the graft to the femur button. The main disadvantage of this technique is that incisions need to be made through the skin and quadriceps muscle resulting in trauma to the leg and a cosmetically undesirable procedure. U.S. Pat. No. 5,645,588 describes an improved technique whereby the ligament anchor may be threaded through a femoral tunnel formed through the femur from the centre of the knee but such still involves the use of sutures attached directly to the fixation device on the outside of the femur above the knee and through which the graft is looped before passing out of the femoral tunnel before being secured to the tibia. Using such techniques inevitably involves the introduction of potential sources of loosening of the graft by way of stretching of the suture. This can cause movement in the graft during subsequent patient mobility which hinders the healing and grafting process. Furthermore, the use of sutures involves the tying of knots which themselves result in some subsequent stretch in the suture, increasing the likelihood that the graft will have inappropriate tension for its intended purpose. The suture itself may also fail under the high tensile forces to which it is subjected during use. PCT/US97/22061 attempts to solve this problem by providing an interference fit insertion element with a proximal apperture through which a graft may be threaded or attached. The technique involves securement of the interference end of the device into the central cancellous area of the bone. Unfortunately, this softer area of the bone may not provide sufficient anchoring of the device to resist the tensions to which the graft is subject in use.
U.S. Pat. No. 5037422 also relates to the anchoring of sutures for securement of a suture to a bore hole in a bone. The device is shown secured to the cancellous bone. The device is for use in soft tissue fixation to the outside of the bone and not fixation within the bore hole itself.
Futhermore, it is not suitable for graft fixation and is only applicable to sutures.
A device for graft fixation using sutures is described in EP 0 619 982 where the anchor includes a body and a plurality of barbs located in axially aligned, circumferentially spaced relation to each other about the body. The barbs have a normal configuration wherein they extend rearwardly and radially outwardly from the anchor body to outer ends which are normally located outside a longitudinal projection of the largest geometric cross-section of the body transverse to its longitudinal axis. The device utilises sutures and suffers from the drawbacks previously outlined. It also relies upon interference between the barbs and the soft cancellous bone area.
According to the present invention there is provided a bone anchor suitable for soft tissue-bone fixation comprising an anchoring member, the anchoring member having a head portion at the distal end thereof and supporting means at the proximal end thereof operable to be urged against the inside surface of the cortical bone, wherein soft tissue locating means are located on the exterior of at least the said head portion.
Advantageously, by having soft tissue locating means on the exterior of the head portion, the soft tissue may be securely located over the exterior of the head to anchor the soft tissue in position. Compression force may then be applied from the trailing ends of the soft tissue urging the support means against the inside surface of the cortical bone through which the hole has been drilled.
A further advantage of the locating means is that it allows the soft tissue to be anchored directly by the anchoring member without the need for interconnecting sutures.
To carry out its function of being urged against the inside surface of the cortical bone in the region around the hole that has been drilled, in use, at least a part of the supporting means is preferably wider or capable of being made wider than the hole that has been drilled.
Preferably, access means are provided in the body of the anchoring member to allow the soft tissue access from the exterior of the member to the hole in the bone.
The access means may be in the form of one or more apertures but, preferably, the supporting means is in the form of a number of legs depending from the head portion and a guide means or spacing between adjacent legs provides access from the exterior of the anchoring member to the hole in the bone.
Preferably, the locating means extends, at least partially, down the outside of the sides of the anchoring member to guide the elongate soft tissue and, preferably, urge it against the walls of the bone hole. Advantageously, this encourages grafting of the soft tissue to the surrounding bone.
Preferably, at least the lowermost portion of the supporting means at the proximal end of the anchoring member extends outwardly to a greater extent than the head portion.
The supporting means may be inwardly radially resiliently deformable at least at the said lowermost portion thereof, so that by compressing the sides of the supporting means radially inwardly, a lowermost portion which is wider than the bone hole may be eased therethrough and, upon release of the compression, the supporting means may then expand inside the hole so that the supporting means may then be urged back against the bone so that the bottom surface at proximal end of the supporting means abuts against the inside surface of the cortical bone in the region around the hole.
The legs may be thickened on the outside thereof at the proximal end to provide the wider lowermost portion of the anchor. Preferably, the anchor member is hollow and the thickness of the bottom surface at the proximal end thereof is such that, in use, the outermost portion of the surface is urged against the inside surface of the cortical bone around the region of the hole whereas the innermost portion of the surface projects over the hole. In this manner, when the proximal end comprises the ends of a number of legs, the gaps between adjacent legs provide access to the hole for tissue guided between adjacent legs. Alternatively, or in addition, the supporting means may be outwardly expandable, preferably, by use of expansion means.
Preferably, the supporting means may be expanded by means of a wedge means or an expansion tool Preferably, the supporting means comprise a number of legs depending from the head portion and the expansion tool or wedge means may be located between the legs to urge the legs radially outwardly with respect to the bone hole. The wedge means may be driven into the anchor means to urge the legs radially outward with respect to the hole. The wedge means may be left in the anchor after use. The wedge means may be in the form of a peg but any suitable shape which could be accommodated by the anchor between the legs may be employed.
Preferably, at least three legs depend from the head portion, more preferably, at least four legs, most preferably, four legs depend from the head portion. The legs may merge together above the lowermost portion and be spaced apart only at the proximal end of the anchoring member.
Preferably, the wedge means is narrower than the hole drilled so that, in use, access to the hole is possible radially outward of the wedge means.
Preferably, the locating means comprises a recessed portion over the distal end of the anchoring member which is suitable to securely locate elongate soft tissue such as tendon, ligament or substitutes therefor. Preferably, the locating means comprises a guide means across the distal end for the elongate soft tissue. Preferably, the recessed portion forms a guide portion for the said elongate soft-tissue. Preferably, there are two such guide means or portions which, preferably, cross each other at the centre of the outside of the said head portion. Preferably, the said two guide portions are substantially at right angles.
The head portion may comprise the distal ends of the legs where the latter merge together at the said distal ends thereof.
Typically, a guide channel is at least partially formed between adjacent legs. At the proximal end, where the legs separate, the channel may be formed by the adjacent sides of neighbouring legs and the wedge means between the said legs.
The head portion may be formed by the merging of the said legs. Preferably, by the merging of at least three such legs, more preferably by the merging of at least four such legs, most preferably, by the merging of four such legs. Preferably, the legs are equidistant.
The recessed portion may be formed by the top surface of the legs, at the distal end thereof. Preferably the top surface of each leg is angled downwardly toward the centre of the head portion to thereby provide the said recessed portion which prevents elongate soft tissue located over the head from sliding off the head in use.
Preferably, the wedge means may be secured in the anchoring member by suitable means to prevent it coming out in use. In some embodiments, the wedge means and inside surface of the legs co-operate in a rib and groove arrangement. The groove may be located on the legs or on the wedge means but to ease entry of the wedge between the legs, the rib is generally located around the wedge means at the proximal end thereof and corresponding grooves are found on the inside of the legs at the proximal end thereof
Preferably, elongate guides extend down the outside of the bone anchor to guide elongate soft tissue, preferably, the guides are recessed into the sides of the bone anchor.
Preferably, the area between the sides of adjacent legs forms an elongate guide to guide the elongate soft tissue from the head portion to the bone hole.
Preferably, the guide is designed to only partially accommodate the full thickness of the elongate soft tissue, so that, in use, the latter is urged against the walls of the hole to encourage grafting thereof.
Preferably, the anchoring member is designed so that a compression force applied at the head portion causes the legs to splay outwardly. Preferably, the bottom surface of the proximal end of the anchoring member legs are distally angled toward the centre line of the anchoring member so that outward splaying of the said legs causes the angle to diminish until the said bottom surface lies substantially in the same plane as the cortical bone against which it abuts. Advantageously, in use, this causes the part of the proximal end in contact with bone to lie flat against the inside surface of the bone for added strength and security. Preferably, in use, the radially outermost part of the bottom surface abuts the region of the inside surface of the cortical bone around the hole and the innermost part extends over the hole in the bone to provide with the adjacent leg an exit hole for the elongate soft tissue and to urge the soft tissue against the cortical bone of the hole to facilitate grafting.
Examples of elongate soft tissue for use with the invention include ligament or tendon, in particular, reconstructed ligament or tendon.
The invention extends to a method of soft tissue-bone fixation utilising the bone anchor. In particular, ligament or tendon fixation at a suitable joint such as the knee, elbow or shoulder. The invention is particularly advantageous in reconstruction of the Anterior Cruciate Ligament (ACL) in the knee or the posterior cruciate ligament (PCL) in the knee. In particular, femoral fixation of the reconstructed ligament. Especially, fixation at the intercondylar notch by mounting the bone anchor on the interior surface of the cortical bone at the intercondylar notch.
According to a second aspect of the present invention there is provided a method of anchoring a graft in a bone comprising the steps of:
forming a tunnel or opening in the bone to a predetermined depth;
securing the graft to the bone anchor so that the trailing ends of the graft extend below the proximal end of the anchor;
inserting the anchor and graft in the tunnel or opening;
and pulling the graft trailing ends to urge the proximal surface of the anchor into contact with the inside surface of the cortical bone around the region of the hole.
Preferably, by pulling the trailing ends, the graft is urged into contact with the walls of the hole.
According to a further aspect there is provided a method of anchoring a bone anchor comprising the steps of:
forming a tunnel or opening in the bone to a predetermined depth;
securing soft-tissue to the anchor;
mounting the bone anchor on the inside surface of the cortical bone;
employing compression means to urge the bone anchor against the said inside surface to provide soft-tissue anchoring.
Preferably, the soft-tissue is elongate and is secured to the anchor so that its trailing ends extend below the proximal end of the anchor.
Preferably, the compression is applied by tensioning the said soft-tissue trailing ends.
Preferably, the soft-tissue is a ligament or tendon graft, more preferably, an ACL or PCL graft.
Preferably, the bone anchor is mounted on the inside surface of the cortical bone at the intercondylar femoral notch, preferably, on the inside surface or distal surface of the cortical bone immediately adjacent the wall of the hole drilled therethrough. The bone anchor may have a plurality of simultaneous mounting points, preferably, at least two, more preferably at least three, most preferably, at least four. Preferably, the mounting points are equally circumferentially spaced with respect to the round hole. Preferably, the mounting points are provided by proximal mounting surfaces at the ends of legs of the bone anchor.
Preferably, the graft is secured to the bone anchor by locating the graft over the outside of a bone anchor according to the first aspect of the invention by placing the graft thereover via the locating means.
Preferably, the method includes the step of locating the graft along the sides of the anchor, preferably, by passing it down elongate guide means located on the side thereof.
Preferably, the method includes the step of expanding the walls of the anchor in the tunnel using wedge means or an expansion tool. Preferably, the wedge is urged up the hollow centre of the anchor to urge the sides outwardly into contact with the walls of the hole and to preferably, provide sufficient contact between the proximal surface of the anchor and the inside surface of the cortical bone so that the anchor is mounted on the said inside surface of the cortical bone.
Preferably, the method includes locating at least two elongate grafts in this manner, preferably, substantially at right angles to each other.
Preferably, the bone anchor comprises bio-compatible materials. For instance, the material may be bio-absorbable material or a non-absorbable permanent material. Such absorbable materials may include trimethylene carbonate copolymers, polylactic acid and polyglycolic acid. Examples of non-absorbable materials include polyethylene, polypropylene, polyester and acetal homopolymers. Alternatively, copolymers of any of the foregoing may be utilised.